1. Field of the Invention
This invention relates to a process for forming metallic alloys having improved material strength and resistance to wear and impact and more particularly to the use of precarburized ferroalloys characterized by fine metallic carbides in a metallic matrix in liquid alloy or steel.
2. Description of the Prior Art
It is well known in the fabrication of cast irons and steels to utilize alloy elements and in particular ferroalloys such as ferrites of niobium, vanadium, molybdenum, titanium, tungsten, chromium and others. These ferroalloys containing carbide and carbonitride forming elements are utilized in small quantities, for example less than 0.5%, in the fabrication of high strength, low alloy steels where the carbon content is low, for example less than 1.0%. The alloy elements are dissolved in the liquid steel resulting in precipitation of carbides and carbonitrides. The precipitation preferably occurs after the solidification. By controlling the grain growth or by precipitation hardening the characteristics of high mechanical strength and toughness are added to the steel.
For the iron base alloys having a carbon content greater than 0.5% and/or alloy elements greater than 0.5% the main function of the alloy elements is to form primary carbides. The alloy elements and the carbon react forming solid carbides which precipitate in the melt. This is desirable in the manufacture of tool steels, high speed steels, heat resistant steels, high carbon steels, high alloy steels and in cast irons. However, the conventional ferroalloys tend to form coarse carbides which impair the alloy properties and specifically the material strength to resist impact. The formation of coarse carbides has been a problem in steel and cast iron making and has overall limited the use of higher amounts of carbide forming alloying elements to achieve the desired properties.
One known solution to the problem of formation of coarse carbides has been the addition of particles or agglomerates of pure, fine powder carbides or powders obtained by other processes. However, this solution is considered economically undesirable.
It is also known in the manufacture of welding electrodes for hard facing to utilize carbides of niobium, vanadium, titanium, tungsten, chromium, molybdenum, and other elements to provide the desired degree of hardness and wear strength. These metals are normally added to the electrodes as ferroalloys. During the deposition, however, a substantial loss of these carbide forming elements is encountered. In the case of titanium the loss approaches 90% and in the case of chromium the loss approaches 25%. Overall the recovery yield of these elements as carbides in the coated material is known to be very low. The process of coating by melting is a high fusion speed one therefore even with an excess of carbon in the electrode, there is insufficient time for complete formation of the carbides. The addition of pure carbides by other processes is considered uneconomical.
In the production of high speed steels and special alloys by powder metallurgy where it is difficult to obtain the desired compositions by melting, use of carbides is known. In these applications the various metallic components are mixed, pressed and sintered until the desired degree of density is reached. To achieve the desired degree of hardness and material strength to resist wear, as in the case of steels, carbides of niobium, vanadium, tantalum, titanium, tungsten, molybdenum, chromium and others are added.
While it is known to utilize ferroalloys containing carbide and carbonitride forming elements in the fabrication of tool steels and other alloy steels, there is a need to achieve increased hardness and wear resistance by the addition of increased amounts of alloy carbides without forming coarse carbides.